It's difficult to tell if robots will ever cross over some line and become, in effect, human.  Humanity suggests a mammal, live birth, not a birth occurring in a lab or a factory.  Even so, the future of humans and machines could look a number of ways.

If scientists, engineers and computer programmers do become able to create machines that are nearly indistinguishable from humans, it seems our society's understanding of what makes something "human" may change or, at least, come up for debate.  Some, in fact, have begun debating the ethical dilemmas that may arise if innovative research continues to develop the cognitive and physical abilities of humanoid robots.  As robots become more autonomous, for example, will we expect them to live by the same laws and regulations that we do?  

It seems doubtful that robots will ever gain the capacity for human emotion.  Already, however, scientists and engineers are developing social humanoid robots that can adjust to new environments, have human-like physical characteristics, and can understand both verbal and non-verbal communication.  The South Korean EveR-1, for example, even has the ability to express a limited set of emotions (joy, anger, sorrow, and happiness) [source: Kim, Sur and Gong].  But being able to express particular feelings does not guarantee that a robot is "just like" a human.  Human beings, after all, often hide their feelings out of fear or desire to be polite.  Will robots ever learn to navigate those difficult social interactions? 

Recognizing that humans learn social cues primarily through experience, researchers in humanoid robotics seek to make machines that develop over time.  These robots learn new words, phrases and the common ways people use them in conversation.  While some of the most sophisticated humanoid robots' conversational skills are still limited, there seems to be great potential for these machines to develop these abilities further. 

Does that mean robots having jobs and earning paychecks? Celebrating birthdays and getting married? Playing with their kids and worrying about finances?

Let's get serious and define "human." The Smithsonian Museum of Natural History distinguishes humans from other life forms by traits that evolved and now characterize humans. We have a common physicality (specific body type that walks upright), engage in social lives, use tools, produce food, employ language and symbols and have complex brains. How do robots measure up, using those benchmarks?

For robot mobility, look at Honda's Asimo, a humanoid robot that can run, change direction and shift its weight. Researchers at the Georgia Institute of Technology, meanwhile, have been developing robots that simulate human motion, moving in a smooth, coordinated manner.

Can robots interact as humans do? MIT Media Lab researchers are trying to replicate aspects of human social behavior in autonomous robots. For instance, after developing a computer game to study cooperation and collaboration, investigators are creating a computer model that will allow robots to engage in teamwork. Nonverbal behavior is also being researched to help robots recognize subtle social cues.

Can robots use tools? NASA's humanoid "robonauts" are built to work side by side with astronauts, employing the same tools. Honda's Asimo can use a tray and cart to transport items. And if robots are able to utilize tools for other jobs, it seems reasonable that they'll be able to plug themselves in or change a battery to obtain "food."

To discuss communication, let's revisit MIT, where the goal is for robots to converse with humans in a natural language. Researchers have created a system so robots can carry on a simple conversation, including answering questions about the past or present and gathering information. Using children's language tests, they measure the robot's development.

True communication wouldn't be possible without a brain, so let's consider IBM's computer, "Watson," which won a "Jeopardy" tournament against human champions. It used natural language to decipher questions, recall information and supply answers quickly. It's not a humanoid robot, but it has advanced artificial intelligence.

If we accept the Natural History Museum's definition of human, it's clear that researchers are developing those facets of robots. However, combining these complex traits within a humanoid robot seems more like science fiction than reality at this point.

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